A liquid crystal display (LCD) device in the prior art includes an LCD panel and a backlight module. Because the LCD panel does not emit light, the backlight module provides a surface light source that emits light uniformly. As shown in FIG. 1, the backlight module includes a light guide panel (LGP) 2, a backplane 1, and a lightbar 3. The lightbar 3 belongs to a line light source. The LGP 2 transforms the line light source to the surface light source used by the LCD panel. As shown in FIG. 2, the lightbar is arranged on a left side of the backlight Because the lightbar is in a shape of a strip, heat for a middle of the lightbar is slowly dissipated and heat for each of two opposite ends of the lightbar is quickly dissipated. Thus, operating temperature of the middle of the lightbar is higher, and operating temperature of each of two opposite ends of the lightbar is lower. Because aging speed and aging degree of the lightbar are directly associated with operating temperature, higher operating temperatures causes aging speed of the lightbar to increase, and causes more serious brightness decay. Because the operating temperature is different, the aging speed and aging degree of each of two opposite ends of the lightbar are different with the aging speed and aging degree of the middle of the lightbar. Thus, brightness is different between two opposite ends of the lightbar and the middle of the lightbar, and light brightness of the entire lightbar is not uniform, finally resulting in that the brightness of two opposite ends of the LGP are bright, and the brightness of the middle of the LGP is dark, which reduces quality of the backlight module.